Many devices today communicate with each other using the IP network. In order to provide mobility support to mobile devices, the IETF (Internet Engineering Task Force) has developed the “Mobility Support in IPv6”, or Mobile IP (see the following Non-Patent Document 1). In Mobile IP, each mobile node has a permanent home domain. When the mobile node is attached to its home network, it is assigned a primary global address known as a home address (HoA).
When the mobile node is away, i.e. attached to some other foreign networks, it is usually assigned a temporary global address known as a care-of address (CoA). The idea of mobility support is such that the mobile node can be reached at the home address even when it is attached to other foreign networks.
This idea is done in Mobile IP with an introduction of an entity at the home network known as a home agent (HA). Mobile nodes register their care-of addresses with the home agents using messages known as Binding Update (BU) messages. This allows the home agent to create a binding between the home address and care-of address of the mobile node. The home agent is responsible to intercept messages that are addressed to the mobile node's home address, and forward the packet to the mobile node's care-of address using packet encapsulation (i.e. putting one packet as the payload of a new packet, also known as packet tunneling).
With the ever-increasing proliferation of wireless devices, it is foreseeable that a new class of mobility technology will emerge. One of such mobility technologies is network mobility, or NEMO, where a whole network of nodes changes its point of attachment in entirety. Extending the concept of mobility support for individual hosts to mobility support for a network of nodes, the objective of a network in motion solution is to provide a mechanism where nodes in a mobile network can be reached by their primary global addresses, no matter where on the Internet the mobile network is attached to.
The IETF is currently developing solution for network mobility as disclosed in the following Non-Patent Document 2. Here, it is specified that the mobile router, when sending BU to its home agent, will specify the network prefix which the nodes in the mobile network are using. These are specified using special options known as Network Prefix Options to be inserted into the BU. These allow the home agent to build a prefix-based routing table so that the home agent will forward any packets sent to destinations with these prefixes to the care-of address of the mobile router. This idea of using a bi-directional tunnel between the mobile router and its home agent is also described in the following Patent Document 1.
Although the bi-directional tunnel allows nodes in a mobile network to be reached no matter where on the Internet the mobile network is currently attached to, it results in traffic between a mobile network node (MNN) and its correspondent node (CN) to go through a sub-optimal route, whereby every packet must go through the home agent. This increases the packet delay which may be unacceptable to real-time multimedia applications, such as Voice-over-IP. Furthermore, if there are multiple mobile networks nesting (i.e. a child mobile router attached behind a parent mobile router), there will be a nesting of bi-directional tunnels as well. This means that for a mobile network node that is nested behind, say, three mobile routers, a packet sent from a correspondent node must go through three home agents before reaching the mobile network node.
To address these concerns, there have been a lot of different proposals of what is known as route optimization. In the following Non-Patent Document 3, a method is disclosed in which mobile routers act as neighbor discovery proxy (hereinafter also referred to as ND-Proxy) its mobile network nodes. The mobile router will configure a care-of address from the network prefix (also referred to as prefix in this description) advertised by its access router, and also relay this prefix to its subnets. When a mobile network node configures an address from this prefix, the mobile router will act as a neighbor discovery proxy on its behalf. In this way, the entire mobile network and its access network form a logical multilink subnet, thus eliminating any nesting.
Hereinafter, the above-mentioned neighbor discovery pr oxy is described referring the network deployment shown in FIG. 1A. In FIG. 1A, a mobile router (MR) 121 is attached to the access router (AR) 111 on the access network link 101. MR 121 gains its connection to the global communication network 100 (such as the Internet) via AR 111. Attached to the access network link 101 is also a mobile node (MN) 130.
Behind the mobile router 121, two mobile routers (MRs) 122 and 123, and a visiting mobile node (VMN) 131 are attached to the mobile network link 141. MR 122 is controlling the mobile network link 142. VMN 132 and a local-mobile network node (LMNN) 152 are attached to the mobile network link 142. MR 123 is controlling the mobile network link 143. VMN 133 and LMNN 153 are attached to the mobile network link 143.
In this description, among nodes (i.e. mobile network nodes (MNNs)) within a mobile network behind a certain MR, a node, whose basic point of attachment is this MR, is referred to as a local mobile network node (LMNN). It is preferable that LMNN configures its address according to the specification of NEMO Basic support (that means a node behind MR configures its address, using a mobile network prefix being advertised by MR from the time that MR connects to its home network).
The idea of neighbor discovery proxy is that MR 121 will advertise the network prefix 171 announced by AR 111 on the access network link 101 to its mobile network link 141. This enables MR 122, MR 123, and VMN 131 to configure their care-of addresses from prefix 171. MR 122 and MR 123 will also advertise prefix 171 to their mobile network links 142 and 143 respectively, thus allowing VMN 132 and VMN 133 to configure their care-of addresses from prefixes 171 as well. Here, VMN is a node within a mobile network which configures its care-of address based on a prefix advertised by MR when connecting to the MR. As the above, LMNN 152 and LMNN 153 have addresses with, the same mobile network prefix as those advertised by MR 122 and MR 123 connecting to their home networks, respectively. Thus, LMNN 152 and LMNN 153 need not reconfigure their addresses due to the change of the prefixes being advertised by MRs after MRs have roamed.
As a neighbor discovery proxy, MR 121 will forward any packet with a source address configured from prefix 171 on the mobile network link 141 to the access network link 101. Conversely, MR 121 will forward packets with a destination address falling within prefix 171 on the access network link 101, to the mobile network link 141. Similarly, MR 122 will forward any packet with a source address configured from prefix 171 on the mobile network link 142 to the mobile network link 141, and forward packets with a destination address falling within prefix 171 on the mobile network link 141 to the mobile network link 142. Again, MR 123 will forward any packet with a source address configured from prefix 171 on the mobile network link 143 to the mobile network link 141, and forward packets with a destination address falling within prefix 171 on the mobile network link 141 to the mobile network link 143.
In this way, from the point of view of CN 160 on the global communication network 100, MR 121, MR 122, MR 123, MN 130, VMN 131, VMN 132 and VMN 133 are all connected to the access network link 101, since they all have care-of addresses configured from the same network prefix 171. This point of view is illustrated in FIG. 1B.
In FIG. 1B, VMN 131 is virtually attached to the access network link 101 through the virtual attachment 183, created by MR 121 performing the neighbor discovery proxy through the mobile network link 141. VMN 132 is also virtually attached to the access network link 101 through the virtual attachment 181, created by MR 122 performing the neighbor discovery proxy through the mobile network link 142. VMN 133 is also virtually attached to the access network link 101 through the virtual attachment 185, created by MR 123 performing the neighbor discovery proxy through the mobile network link 143. In this way, MN 130 and VMN 131, VMN 132 and VMN 133 can use the standard Mobile IPv6 Route Optimization technique specified in the Non-Patent Document 1 to communicate with CN 160.
[Non-Patent Document 1] Johnson, D. B., Perkins, C. E., and Arkko, J., “Mobility Support in IPv6”, Internet Engineering Task Force Request For Comments 3775, June 2004.
[Non-Patent Document 2] Devarapalli, V., et. al., “NEMO Basic Support Protocol”, IETF. RFC 3963, January 2005.
[Non-Patent Document 3] Jeong, J., et. al., “ND-Proxy based Route Optimization for Mobile Nodes in Mobile Network”, IETF Internet Draft: draft-jeong-nemo-ro-ndproxy-02.txt, February 2004, expired.
[Patent Document 1] U.S. Pat. No. 6,636,498
[Patent Document 2] U.S. Patent Application Publication 2005/0144330
[Patent Document 3] U.S. Patent Application Publication 2005/0036471
[Patent Document 4] PCT Application Publication WO2005/048512.
Although the above-mentioned neighbor discovery proxy disclosed in the Non-Patent Document 3 seems an elegant way to solve the route optimization problem for network mobility support, there is one main limitation: whenever the mobile network changes its point of attachment, the prefix announced by the access router has changed, and every node in the mobile network using the prefix announced by the access router based on the neighbor discovery proxy must now re-configure their care-of addresses.
It is possible that, behind MR implementing both the neighbor discovery proxy and network mobility support, there are LMNNs and nodes which have configured their addresses using the prefix announced by the access router MR is connecting to. As the above, nodes which need to re-configure their addresses due to the movement of MR are those which have configured their addresses using the prefix announced by the access router MR is connecting to, such as VMN 131-133, MR 122 and MR 123 which need to change the prefix of their addresses from the prefix 171 to the prefix 172 when MR 121 changes its point of attachment from AR 111 to AR 112.
Current IPv6 address configuration uses two main approaches: address: auto-configuration and dynamic host configuration. In address auto-configuration, a node is supposed to generate an IP address based on its hardware address and the announced prefix, and perform a procedure known as Duplicate Address Detection (DAD) to ascertain that the address it has generated is unique. DAD requires the node to send out at least one Neighbor Solicitation (NS) broadcast message. In dynamic host configuration approach, a node sends out an address request broadcast message. A server would respond to this request by assigning an address to the node. This is also known as the Dynamic Host Configuration Protocol (DHCP).
In both approaches of address auto-configuration and dynamic host configuration, a node needs to send out at least one broadcast message. So, when a large mobile network changes its point of attachment, the number of messages generated will be enormous and simultaneous. This may cause temporary congestions and further delay in the address configuration.
Hereinafter, this problem will be described referring to the example of composition in FIG. 1A and FIG. 1B. When MR 121 moves from an access network link 101 to an access network link 102, it will receive a new access network prefix 172 being announced by AR 112. This will not only cause a change in the care-of address of MR 121, it will also cause MR 122, MR 123, VMN 131, VMN 132 and VMN 133 to change their care-of addresses. Due to the need for DAD, each of these nodes need to send out a Neighbor Solicitation message, which MR 121, MR 122 and MR 123 operating as neighbor discovery proxies, need to forward to an access network link 102, mobile network links 141, 142 and 143.
This problem of DAD has been addressed by various teachings in the prior art. In the technology disclosed by the Patent Document 2, the home agent of a mobile node is used to resolve the conflict of the mobile node's home address. In the technology disclosed by the Patent Document 3, a fast DAD entity is introduced in a distributed system to rapidly resolve address conflicts of mobile nodes in the foreign network. In the technology disclosed by the Patent Document 4; mobile network nodes optimally communicate with an address and prefix delegating entity in the foreign network. None of these technologies disclosed by the Patent Documents 2-4 can substantially ease the burst of traffic due to signaling (large volume of traffic streaming within a short period) when a mobile network using the neighbor discovery proxy method disclosed in the Non-Patent Document 3 changes its point of attachment.
A person skilled in the art would also appreciate that even though the neighbor discovery proxy method for route optimization is specifically illustrated in this description, other route optimization schemes may have similar signaling burst problems as well. For instance, it is possible to use Hierarchical Mobile IPv6 technology to provide nested tunnel optimization. Here, every mobile network node would obtain a regional care-of address from the mobility anchor point (which may be a fixed or mobile router). All mobile network nodes would need to change their regional care-of addresses when the mobile network changes to a different mobility anchor point, thus causing a massive amount of binding update messages being sent.